JP2005-93196A discloses a conventional example of a lighting device which is configured to be connected to a light source device including a light-emitting device (such as a light-emitting diode) and to light the light-emitting device of the light source device. The lighting device of the conventional example is configured to be connected to a light source device selected from predetermined two or more light source devices that have different rated currents.
In the conventional example, each of the two or more light source devices is provided with a resistor connected in parallel to a light-emitting device thereof, and the resistors of the two or more light source devices have different impedance (different resistance values) in accordance with the rated currents of the light sources.
Also, the lighting device of the conventional example is configured, before starting lighting a light-emitting device of a light source device connected thereto, to supply the light source device with a small current so as not to light the light-emitting device, and to measure a voltage drop in the light source device (i.e., measure a voltage drop across a resistor of the light source device). The lighting device is configured to identify a rated current of the light source device connected to the lighting device based on the measured voltage drop, and to supply the light source device with the identified rated current.
In a lighting device which is configured to identify a light source device connected thereto based on a voltage drop across a resistor (i.e., based on an impedance of the resistor) as in the conventional example, there is however a problem that the lighting device is liable to make wrong identification of a connected light source device owing to noise and/or fluctuation in impedance of the resistor caused by temperature fluctuation.